UTGE 


UNIVERSITY  OF  WISCONSIN 
COLLEGE  OF  ENGINEERING 

ENGINEERING  EXPERIMENT  STATION 

Contributions  from  the 
Department  of  Steam  and  Gas  Engineering 

TESTS  ON  THE  RECIRCULATION  OF 
WASHED  AIR 

BY 

GUSTUS  L.  LARSON 

Associate  Professor  of  Steam  and  Gas  Engineering 


Reprinted  from  the  Transactions  of  the 
American  Society  of  Heating  and  Ventilating  Engineers 
Vol.  22,  pp.  11-51 

MADISON 

1916 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/testsonrecirculaOOIars 


« 


W 1/ 


ALTGELD  KALL 


TESTS  ON  THE  RECIRCULATION  OF  WASHED  AIR 
By  G.  L.  Larson* 

INTRODUCTION 


In  the  light  of  more  modern  studies  in  ventilation  it  would 
seem  that  the  real  explanation  of  the  ill  effects  of  bad  ventilation 
as  not  to  be  found  in  the  chemical  composition  of  the  atmosphere 
breathed.  The  long  debated  idea  that  expired  air  contains  or- 
ganic matter  which  is  toxic  has  been  abandoned  by  most  physiolo- 
gists. 

The  various  phases  of  the  chemical  composition  of  air  were 
discussed  some  time  ago  in  a symposium  on  ventilation  at  the 
Chemist’s  Club  in  New  York  City. 

There  is  unanimity  among  them  regarding  the  chemical  viti- 
ation of  the  air.  Pure  air  contains  nearly  21%  of  oxygen.  This 
may  be  reduced  to  17%,  a proportion  too  small  even  to  support 
ordinary  combustion,  before  its  diminution  becomes  harmful. 
Except  in  extreme  conditions  the  amount  of  oxygen  in  the  closest 
halls  crowded  with  people  practically  never  falls  below  20%. 
Oxygen  will  therefore  take  care  of  itself  and  may  probably  be 
wholly  left  out  of  consideration  in  ventilating  systems.  We  are 
reminded  that  it  is  necessary  to  go  only  a short  distance  up  into 
the  mountains  to  come  under  an  atmospheric  pressure  such  as  to 
reduce  the  oxygen  supply  much  more  than  it  is  reduced  in 
crowded  assemblies,  and  yet  mountain  air  is  especially  healthful. 

The  air,  under  usual  conditions,  contains  about  4 parts  of  car- 
bon dioxide  per  ten  thousand  parts  (0.04  per  cent.)  and  the 
“standard”  of  desired  purity  for  the  air  of  dwellings  was  long 
placed  as  low  as  6 parts  per  ten  thousand.  Experimentation  in- 
dicates, however,  that  it  does  not  become  harmful  to  man  until  the 
carbon  dioxide  accumulates  to  above  one  per  cent.,  or  nearly 
forty  times  its  usual  amount.  The  air  in  crowded  rooms  very 
rarely  reaches  0.4  per  cent.,  so  that  evidently  a quantity  of  car- 


Associate  Professor  of  Cas  and  Steam  Engineering,  University  of  Wisconsin. 


4 


Tests  on  the  Recirculation  of  Washed  Air 


bon  dioxide  far  exceeding  the  highest  hygienic  limit  which  has 
hitherto  been  set  up  as  a “standard”  can  be  breathed  with  impu- 
nity. It  has  also  been  stated  that  the  bacteria  in  the  air  need  not 
be  considered  in  the  problem  of  ventilation,  since  the  comparative 
unimportance  of  the  air  as  a vehicle  of  infection  is  becoming 
widely  recognized.  (See  Journal  of  the  American  Medical  Asso- 
ciation, “The  Air  as  a Vehicle  of  Infection.”  Feb.  7,  1914,  p.  423.) 

In  contrast  with  all  the  foregoing  negative  factors  with  respect 
to  the  discomfort  or  ill  health  hitherto  associated  with  inadequate 
ventilation,  we  may  now  conclude  with  reasonable  certainty  that 
the  symptoms  of  discomfort  in  a badly  ventilated  place  are  due 
to  the  physical  condition  of  the  air  with  respect  to  temperature, 
humidity  and  movement,  and  not  to  any  chemical  properties 
whatever.  (The  Journal  of  the  American  Medical  Association, 
Nov.  7th,  1914.) 

The  university  engineers  had  the  above  points  in  mind  in 
designing  the  ventilating  systems  of  the  Wisconsin  High  School, 
and  the  tests  herein  described  were  undertaken  in  order  to  ascer- 
tain the  advisability  of  installing  similar  systems  in  the  future 
buildings  of  the  University. 

The  system  was  designed  by  J.  M.  Smith,  Operating  Engineer 
of  the  University  Heating  Station,  under  the  supervision  of  Prof. 
H.  J.  Thorkelson,  Consulting  Engineer  for  the  University. 

The  tests  were  undertaken  especially  with  a view  of  throwing 
light  upon  the  following  questions  : 

1.  What  constitutes  good  ventilation? 

2.  Is  proper  ventilation  a problem  of  supplying  large  volumes 
or  merely  a question  of  higher  velocities  with  properly  regulated 
humidity  and  temperatures? 

3.  Does  recirculation  give  efficient  as  well  as  economical  ven- 
tilation ? 

4.  What  is  the  effect  of  the  washer  upon  the  bacteria  and 
carbon  dioxide  content  of  the  air? 

The  writer  desires  to  express  his  thanks  to  Prof.  H.  J.  Thorkel- 
son for  his  valuable  advice  and  encouragement  and  to  Prof.  Wm. 
Black  for  his  advice  and  assistance  at  various  times.  He  is  also 
indebted  to  Mr.  J.  M.  Smith,  Operating  Engineer,  and  to  Messrs. 
Bauer  and  Blanding,  of  the  Senior  Class  in  Mechanical  Engineer- 
ing, for  valuable  assistance  rendered  in  preparing  for  and  conduct- 
ing the  tests.  The  writer  desires  especially  to  express  his  thanks 
to  Mr.  E.  J.  Tully,  Chemist,  State  Laboratory  of  Hygiene,  for  his 
hearty  co-operation  and  valuable  assistance  in  conducting  the 
bacteria  tests. 


Tests  on  the  Recirculation  of  Washed  Air 


5 


6 


Tests  on  the  Recirculation  of  Washed  Air 


DESCRIPTION  OF  BUILDING  AND  EQUIPMENT 

In  preparation  for  the  tests  herein  recorded  some  preliminary 
tests  were  made  on  a small  air  washer  and  recirculating  system 
which  was  built  for  experimental  purposes  and  installed  in  one 
of  the  rooms  in  the  Engineering  Building.  With  this  apparatus 
it  was  almost  impossible  to  duplicate  conditions  as  found  in  prac- 
tice and  as  the  tests  were  of  a preliminary  nature  only,  their 
results  will  not  be  recorded  in  this  treatise. 

The  tests  which  will  be  described  here  were  made  at  the  Uni- 
versity of  Wisconsin  High  School.  This  is  the  newest  of  the 
buildings  on  the  Wisconsin  Campus,  being  used  for  the  first  time 
at  the  beginning  of  the  present  school  year.  Figure  I shows  a 
view  of  this  building.  It  is  substantially  built  of  Bedford  stone 
and  pressed  brick,  and  equipped  with  steel  window  frames  and 
sash.  Each  window  has  at  least  one  venting  panel  and  the  win- 
dows in  the  first,  second  and  third  stories  have  two  such  panels. 

These  panels  are  designed  with  double  contacts  to  insure  clos- 
ing exactly  to  prevent  the  passage  of  air.  Only  the  south  and 
middle  portions  of  the  building  have  been  constructed,  the  north 
wall  being  left  in  a condition  to  facilitate  future  extension. 

SYSTEM  OF  HEATING 

The  building  is  heated  with  8,530  square  feet  of  direct  radia- 
tion with  the  addition  of  516  square  feet  of  indirect  radiation 
placed  between  the  washer  and  the  fan.  The  system  is  of  the 
one  pipe,  direct  steam  type  throughout.  The  direct  radiators  are 
of  the  Peerless  pattern  and  they  are  supported  on  the  walls  by 
iron  brackets.  The  indirect  radiators  are  of  the  Vento  cast  iron 
type.  This  indirect  radiation  consists  of  four  radiators  set  two 
radiators  high  and  two  wide  and  valved  with  hand  valves  in  such  a 
manner  that  one,  two,  three  or  all  the  radiators  may  be  used  as 
needed.  The  radiators  are  placed  at  such  a height  that  ample 
space  is  left  beneath  them  for  by-passing  the  air  to  the  fan. 

All  of  the  radiators  in  the  building,  including  the  indirect  coils 
and  by-pass  damper,  are  controlled  by  the  national  automatic 
temperature  control  system.  All  air  controlled  valves  on  radia- 
tors are  equipped  with  hand  screw  and  lock  shield  stems  for 
permitting  the  valves  to  be  closed  by  hand,  so  that  in  mild 
weather  any  of  these  radiators  may  be  cut  out. 

Steam  is  delivered  to  the  building  through  a tunnel  from  the 
University  Heating  Plant. 


Tests  on  the  Recirculation  of  Washed  Air 


7 


SYSTEM  OF  VENTILATION 

The  ventilation  of  the  building  consists  of  a blast  fan  dis- 
charging through  ducts  on  the  ceiling  of  the  basement  and  rising 
to  the  rooms  to  be  ventilated,  entering  the  rooms  near  the  ceil* 
ing.  The  vent  ducts  leave  the  rooms  near  the  floor  and  are 
carried  down  to  a system  of  tunnels  below  the  basement  floor 
which  carry  the  air  back  to  the  fan  through  an  air  washer  and 
indirect  radiators.  A sliding  adjustable  door  is  provided  in  the 
housing  ahead  of  the  air  washer  for  the  admission  of  outside 
air  when  necessary. 

The  toilet  rooms  are  ventilated  by  a system  of  exhaust  venti- 
lation consisting  of  an  exhaust  fan  in  the  attic  and  a system  of 
ducts  leading  from  the  toilet  rooms  to  the  fan  with  a connection 
to  each  closet  fixture. 

The  ventilation  of  the  Chemical  Laboratory  consists  of  an  ex- 
haust fan  in  the  attic  with  a duct  leading  to  the  Chemical  Labora- 
tory on  the  third  floor.  This  duct  has  a register  at  both  the  floor 
and  the  ceiling.  The  exhaust  fans  discharge  through  globe  vents 
on  the  roof. 

The  general  ventilation  of  the  building  is  furnished  by  a No.  13 
multi  vane  blast  fan  rated  at  165  R.  P.  M.  direct  connected  to  a 
10  H.  P.  500  volt  direct  current  motor.  The  fan  is  rated  to  de- 
liver 32,400  cubic  feet  per  minute  against  a pressure  of  24  an 
inch  of  water.  The  speed  of  the  motor  can  be  varied  by  field  con- 
trol. 

The  air  washer  is  a Thomas  “Acme”  type.  This  washer  con- 
sists of  a spray  chamber  equipped  with  sufficient  spray  nozzles 
of  approved  type ; a settling  tank  supplied  with  a float  valve, 
connected  to  the  LTniversity  water  main,  to  maintain  the  water 
level  and  also  an  overflow  and  drain  pipe  connected  to  the  sewer. 
It  is  equipped  with  a centrifugal  pump  which  takes  its  suction 
from  the  settling  tank  and  discharges  through  a basket  strainer, 
to  the  spray  nozzles.  The  eliminators  are  of  the  vertical  type. 
The  pump  is  direct  connected  to  a 500  volt  direct  connected 
motor. 

The  entire  system  is  designed  with  the  view  of  future  enlarge- 
ment of  the  building  and  the  capacity  of  the  apparatus  is  suffi- 
cient to  supply  the  entire  building  when  completed.  The  ducts 
and  tunnels  are  arranged  so  that  the  future  wing  of  the  building 
can  be  connected  directly  to  the  present  system. 


8 


Tests  on  the  Recirculation  of  Washed  Air 


DESCRIPTION  OF  THE  APPARATUS  AND  METHODS  USED 
Steam  and  Power  Consumption  Tests 

The  condensed  steam  from  the  building  was  taken  directly 
from  the  steam  traps  and  weighed.  The  condensate  from  the 
traps  was  at  a temperature  of  about  210  degrees  and  it  became 
necessary  to  run  it  through  a condenser  barrel  to  prevent  loss 
from  evaporation.  Figure  II  is  a view  of  the  arrangement  of  bar- 


Fig.  III. 


Tests  on  the  Recirculation  of  Washed  Air 


9 


rels  and  scales  used.  Figure  III  is  the  same  view  with  the  barrels 
and  scales  removed  to  show  the  condenser  barrel  and  the  steam 
traps.  This  view  also  shows  the  main  steam  line  entering  the 
building  from  the  tunnel  and  the  return  piping.  Calibrated  me- 
ters of  a standard  make  were  used  to  measure  the  power  con- 
sumption of  the  fan  and  washer  motors. 

No  particular  difficulty  was  experienced  in  weighing  the  con- 
densate except  that  it  was  impossible  to  get  a steady  and  uniform 
flow.  This  was  undoubtedly  due  to  the  intermittent  action  of 
the  thermostats  and  possibly,  in  some  degree,  to  sticking  of  the 
steam  traps. 


AIR  MEASURING  APPARATUS 

An  anemometer  was  used  to  measure  the  air  velocities.  Since 
these  instruments  are  often  very  unreliable  great  care  was  taken 
to  calibrate  it  properly.  A special  apparatus  was  built  for  per- 
forming this  calibration.  It  consists  of  a stand  with  a movable 
arm  of  such  a radius  that  the  anemometer  moves  around  a circle 
twenty  feet  in  circumference  with  one  revolution  of  the  arm.  By 
means  of  a belt  and  pulleys  any  speed  desired  can  be  obtained.  A 
lever  arm  on  top  of  the  stand  is  for  starting  and  stopping  the 
recording  mechanism  of  the  anemometer  when  the  movable  arm 
which  carries  the  anemometer  is  in  motion. 

Considerable  difficulty  was  met  in  getting  the  true  volume  of 
the  air  entering  the  rooms.  This  will  be  explained  later. 

CARBON  DIOXIDE  APPARATUS 

Haldane’s  Portable  apparatus  was  used  to  measure  the  carbon 
dioxide  contained  in  the  air.  This  apparatus  is  easily  operated, 
and,  while  it  is  not  the  most  accurate  one  on  the  market  for 
measuring  small  amounts  of  carbon  dioxide,  it  is  accurate  enough 
for  most  conditions  met  with  in  practice. 

Haldane,  in  his  book,  “Methods  of  Air  Analysis,”  states  that 
his  portable  carbon  dioxide  apparatus  will  not  vary  more  than 
one-half  of  one  part  in  ten  thousand  either  side  of  the  correct 
result.  The  writer  checked  the  apparatus  at  various  times  by 
measuring  the  carbon  dioxide  contained  in  the  outside  air,  and 
at  no  time  did  the  readings  vary  more  than  the  above  mentioned 
amount.  It  is  safe  to  say  that  even  with  a little  practice,  read- 
ings can  be  obtained  which  will  not  vary  more  than  one  part  in 
ten  thousand  either  side  of  the  correct  residt. 


10 


Tests  on  the  Recirculation  of  Washed  Air 


APPARATUS  FOR  BACTERIA  TESTS 

Two  different  methods  were  used  to  obtain  a count  of  the 
number  of  bacteria  in  the  air.  The  first  consisted  of  drawing  a 
measured  amount  of  air  through  a sugar  or  sand  filter.  No  con- 
sistent results  were  obtained  from  the  use  of  sugar  filters.  The 
moisture  in  the  air  caused  the  sugar  to  stick  to  the  inside  of 
the  filter  tubes  and  it  was  removed  with  considerable  difficulty. 
The  time  required  to  take  samples  varied  very  greatly  with  the 
sugar  filters. 

The  sand  filters  gave  very  consistent  results  as  will  be  seen 
later. 

The  second  method  consisted  in  the  use  of  Petrie  dishes  and 
most  of  the  bacteria  tests  were  made  in  this  way. 

APPARATUS  FOR  TRACING  AIR  CURRENTS 

Several  methods  were  used  for  tracing  the  air  currents  in  the 
rooms.  The  common  method  of  using  ammonia  and  tumeric 
paper  was  tried  but  the  change  in  color  of  the  tumeric  paper  from 
yellow  to  pink  was  so  gradual  that  it  was  next  to  impossible  to 
tell  when  the  action  commenced.  Both  of  the  other  methods 
used  were  quite  successful. 

Instead  of  using  ammonia  and  tumeric  paper,  hydrogen  sul- 
phide and  lead  acetate  were  used.  A rubber  tube  from  the  hydro- 
gen sulphide  generator  was  placed  in  the  incoming  duct  and  filter 
papers  dipped  in  lead  acetate  were  placed  in  various  parts  of  the 
room.  The  filter  papers  turned  black  almost  immediately  upon 
coming  in  contact  with  the  hydrogen  sulphide  gas.  The  odor 
of  the  hydrogen  sulphide  gas  makes  it  inconvenient  to  use  it, 
but  on  the  whole  it  is  fully  as  satisfactory  .as  ammonia. 

The  air  currents  were  also  traced  by  using  very  light  stream- 
ers of  silk  floss.  This  method  proved  very  successful  as  very 
slight  air  currents  can  be  traced  in  this  way. 

OBSERVATIONS 

Air  Measurements 

As  has  been  stated  before,  considerable  difficulty  was  met  with 
in  getting  the  true  volume  of  air  entering  the  rooms. 

Readings  were  taken  at  the  ducts  leading  to  the  gymnasium. 
First  a series  of  readings  were  taken  at  the  register  and  then  the 
register  was  removed  and  another  set  of  readings  taken  holding 
the  anemometer  horizontally  in  the  vertical  duct  leading  to  the 


Tests  on  the  Recirculation  of  Washed  Air 


11 


loom.  The  readings  at  the  register  showed  an  average  of  482 
feet  per  minute  and  those  in  the  duct  showed  an  average  of  810 
feet  per  minute. 

The  registers  are  unusually  heavy  and  the  net  area  of  the  par- 
ticular size  in  the  gymnasium  is  only  96%  of  the  area  of  the 
vertical  duct  leading  to  the  room.  Therefore  the  velocity  through 
the  register  should  check  very  closely  with  the  velocity  in  the 
duct,  which  is  very  far  from  being  the  case  as  shown  above. 

Further  readings  were  taken  in  a room  which  had  a horizontal 
duct  leading  to  it  so  that  the  anemometer  could  be  left  standing 
in  the  duct  and  readings  taken  after  the  register  had  been  re- 
placed. 

In  this  room  the  velocity  at  the  register  was  386  ft.  per  minute ; 
the  velocity  in  the  duct,  with  the  register  removed,  was  944  ft. 
per  minute ; and  the  velocity  in  the  duct  after  the  register  was 
replaced  was  828  ft.  per  minute.  In  this  room'  the  net  area  of  the 
register  is  88%  of  the  area  of  the  duct  leading  to  the  room.  Note 
that  the  ratio  of  velocities  in  the  duct,  with  and  without  the 
register  in  place,  is  828/944  or  87.7%.  As  a check  upon  the  above, 
readings  of  a similar  nature  were  taken  in  another  room.  This 
room  also  had  a horizontal  duct  leading  to  it  so  that  the  anemom- 
eter could  be  placed  in  the  duct  behind  the  register.  Here  the 
ratio  of  the  velocities  in  the  duct  with  and  without  the  register 
in  place  was  86.8%  and  the  ratio  of  the  velocity  at  the  register 
to  that  in  the  duct  was  only  35.7%.  The  net  area  of  the  register 
was  88%  of  the  area  of  the  duct. 

These  tests  show  conclusively  that  the  register  deflected  the 
air  currents  in  such  a manner  as  to  give  velocity  values  which 
were  very  much  lower  than  the  actual  values,  and  that  readings 


12 


Tests  on  the  Recirculation  of  Washed  Air 


taken  with  the  anemometer  placed  against  the  register  are  abso- 
lutely unreliable. 

The  above  is  a sketch  of  a portion  of  one  of  the  registers. 
They  are  made  of  pressed  steel  and  the  section  at  AB  shows  the 
form  of  the  stampings. 

The  concave  surface  of  the  meshes  will  of  course  set  up  swirls 
in  the  air  current  but  it  would  only  be  a guess  to  say  what  gen- 
eral direction  they  would  take.  As  in  hydraulic  work,  there  will 
probably  be  a contraction  of  the  air  current  after  it  has  passed 
between  the  meshes. 

But  in  accounting  for  the  low  velocities  obtained  when  the  ane- 
mometer was  held  against  the  register  face,  it  must  be  borne  in 
mind  that  an  anemometer  is  calibrated  under  conditions  where 
the  air  strikes  with  equal  intensity  over  the  entire  surface  of  the 
vanes. 

In  a register  such  as  the  above,  56%  of  the  face  is  composed  of 
the  meshes. 

These  meshes  create  a great  number  of  dead  air  spaces,  and, 


Tests  on  the  Recirculation  of  Washed  Air 


13 


while  the  velocity  through  the  meshes  may  be  the  same  as  the 
velocity  in  the  riser,  the  anemometer  will  not  show  it  because  the 
vane  area  effected  is  much  less  than  the  vane  area  effected  under 
calibrating  conditions. 

Velocity  measurements  were  taken  in  all  rooms.  The  results 
are  tabulated  in  Table  I.  The  registers  were  removed  in  each 
case  and  enough  readings  taken  in  the  duct  to  giv,e  a fair  average. 
The  volumes  were  obtained  by  multiplying  this  average  velocity 
by  the  net  area  of  the  register.  That  this  method  gives  a fair 
value  was  shown  later  by  velocity  measurements  taken  at  the 
suction  side  of  the  fan  and  in  the  two  return  tunnels  from  the 
rooms.  Referring  to  Table  I it  will  be  seen  that  the  total  volume 
supplied  to  all  the  rooms  was  15,241  cubic  feet  per  minute.  The 
readings  taken  at  the  suction  side  of  the  fan  gave  a volume  of 

Table  I 

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^Obtained  bv  negiectins  store  rooms  and  boom3i2 


14 


Tests  on  the  Recirculation  of  Washed  Air 


15,000  cubic  feet  per  minute  and. the  readings  in  the  return  tunnels 
gave  a volume  of  14,120  cubic  feet  per  minute. 

fable  I shows  that  the  velocity  of  the  air  entering  the  rooms 
ranged  from  139  to  918  feet  per  minute  with  an  average  of  607 
feet  per  minute.  This  average  is  about  double  the  velocity 
usually  recommended  and  in  the  opinion  of  the  writer  it  is  one 
of  the  desirable  features  of  the  system. 

The  volume  of  air  supplied  per  student  is  low  compared  with 
the  amount  that  would  have  to  be  supplied  on  the  old  basis  of 
keeping  the  carbon  dioxide  content  down  to  six  parts  in  ten 
thousand.  The  cubic  feet  of  air  per  student  varies  from  5.8  to 
25.5  with  an  average  of  13.6. 

This  seems  low  to  one  accustomed  to  the  old  figure  of  30  cubic 
feet  of  air  per  student  per  minute  but  the  air  in  the  rooms  always 
seemed  fresh  and  clean  and  the  amount  supplied  was  apparently 
ample.  (See  questionaire  submitted  to  the  teachers  in  the  build- 
ing.) 

STEAM  CONSUMPTION  TESTS 

Three  steam  consumption  tests  were  made,  of  24,  24  and  27 
hours’  duration,  respectively. 

The  condensed  steam  was  weighed  every  fifteen  minutes  and 
all  temperature  readings  were  taken  every  half  hour.  Power 
readings  and  humidity  readings  were  also  taken  every  half  hour. 
The  summarized  steam  weights  and  temperatures  are  given  in 
Tables  II,  III  and  IV.  Figures  IV,  V and  VI  are  graphical  logs 
plotted  from  Tables  II,  III  and  IV.  The  Vento  heaters  in  the 
housing  were  not  in  use  during  any  of  the  tests.  There  was  no 
steam  on  them  and  the  condensation  weighed  from  them  was 
only  leakage  through  the  valves. 

Test  No.  1 was  started  at  7:00'  A.  M.,  February  2nd,  and  con- 
tinued to  7 :00  A.  M.,  February  3rd.  February  2nd  was  dark  and 
cloudy  and  there  was  not  much  temperature  variation  during  the 
twenty-four  hours.  The  highest  average  outside  temperature 
was  29.6°  and  the  lowest  was  22.1°  with  an  average  of  26.6°. 
The  average  inside  temperature  was  67.1°  and  the  average 
pounds  of  steam  per  hour  per  degree  difference  in  temperature 
between  the  outside  and  inside  was  24.1.  The  graphical  log  shows 
clearly  the  relation  between  the  hourly  steam  consumption  and 
the  outside  temperature.  Notice  the  effect  of  the  fan  upon  the 
steam  rate  curve.  There  was  a sudden  decrease  in  steam  con- 
sumption soon  after  the  fan  started  and  an  increase  immediately 
after  the  fan  was  stopped.  This  is  also  shown  in  the  curve  of 
steam  consumption  per  hour  per  degree  difference. 


Tests  on  the  Recirculation  of  Washed  Air 


15 


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16 


Tests  on  the  Recirculation  of  Washed  Air 


table  iii-a. 

Faph  amdAir  Washer  Log 

FEOM  7JOAM  TO  3:30  PM.  PER  20.  / SIS.  TEST  NO.  2. 


T IME 

Motor  Logs 

Fam  a/nd  Washer  Log 

Fam  Motor 

Pump 

Motor 

Temperatures 

Humidity 

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56 

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65.5 

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174 

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7.9 

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173 

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7.9 

4.65 

58 

66 

397 

60 

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58 

62 

98 

12:30 

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4.75 

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174 

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8.0 

4.80 

58, 

66 

39.7 

60 

60 

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62 

98 

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175 

525 

80 

4.73 

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174 

325 

82 

5.00 

58 

66 

59.5 

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60 

59 

62 

97 

230 

176 

525 

8.5 

5.20 

3:00 

173 

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5.00 

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66 

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60 

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5.00 

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100 

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174 

518 

8.0 

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5 as 

60 

573 

585 

944 

Table  II-A 

Fam  amd  Air  Washer  Log 


rBOM  730  A M.  TO  330  PM.  FEB.  2 IOI.S TEST  No.  1 


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HUMIDITY 

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172 

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565 

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300 

173 

530 

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425 

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430 

59 

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59 

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58. 

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59 

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61.5 

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62 

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58 

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665 

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330 

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Tests  on  the  Recirculation  of  Washed  Air 


17 


8.00  9.00  10.00  I 100  12.00  LOO  200  3.00  4.00  5.00  6.00  7.00  8.00  9.00  10.00  I LOO  1200  LOO  200  3.00  4.00  5.00  6.00  7.00 

Fig.  4 


18 


Tests  on  the  Recirculation  of  Washed  Air 


8.00  9.00  10.00/ 1.00  12-00  LOO  2 00  3.00  4.00  5.00  6.00  7.00  8.00  9.00  10.00  I LOO  12-00  LOO  2-00  3.00  4.00  500  600  700 

Fig-5 


Tests  on  the  Recirculation  of  Washed  Air 


19 


20 


Tests  on  the  Recirculation  of  Washed  Air 


In  all  three  tests  there  are  irregularities  in  the  steam  consump- 
tion curve  which  can  only  be  accounted  for  as  resulting  from  the 
intermittent  action  of  the  thermostats,  or  from  lack  of  positive 
action  in  the  steam  traps.  At  times  the  condensed  steam  would 
almost  cease  to  flow  and  then  would  suddenly  flow  out  in  large 
quantities.  If  these  high  points  were  spread  out  over  several 
readings  preceding  them  the  curve  would  give  a better  idea  of 
the  actual  relations  existing. 

For  a more  technical  discussion  of  the  exact  results  of  these 
tests  see  Chapter  on  “Calculations.” 

Test  No.  1 showed  such  a decided  drop  in  steam  consumption 
after  the  fan  had  started  that  it  was  thought  advisable  to  check 
the  results  with  a duplicate  run.  In  Test  No.  1 the  fan  was  start- 
ed thirty  minutes  after  the  test  was  started  and  it  was  impossible 
to  tell  just  what  effect  it  had  on  the  general  shape  of  the  curve. 
To  overcome  this  difficulty  the  second  test  was  started  12 y2 
hours  before  the  fan  was  started. 

Test  No.  2 was  started  7 :00  P.  M.  February  27th  and  continued 
to  7:00  P.  M.  February  28th.  February  27th  was  a bright  and 
sunny  day  as  was  also  February  28th.  The  average  outside  tempera- 
ture ranged  from  17.9°  to  39.4°  with  a total  average  of  26°.  The 
extreme  range  of  the  outside  thermometers  varied  from  a mini- 
mum of  16.5°  to  a maximum  of  50°.  The  average  inside  tem- 
perature (inside  wall)  was  66.8  degrees  and  the  average  pounds 
of  steam  per  hour  per  degree  difference  was  17.2.  The  graphical 
log  shows  the  effect  of  the  fan  on  the  steam  consumption.  There 
was  a small  drop  in  steam  consumption  due  to  the  fan  but  not 
nearly  as  much  as  was  shown  in  Test  No.  1.  In  Test  No.  2 the 
steam  consumption  continued  to  decrease  after  the  fan  had  stop- 
ped. This  is  probably  due  to  the  fact  that  the  average  outside 
temperature  curve  was  still  rising  and  that  the  walls  must  have 
absorbed  considerable  heat  from  the  high  temperature  on  the 
sunny  side  in  the  afternoon. 

In  the  test  just  described  thermometers  were  hung  in  the 
middle  of  the  rooms  as  well  as  near  the  inside  wall  of  the  rooms. 
It  is  interesting  to  note  the  effect  of  the  fan  upon  the  heat  distribu- 
tion as  shown  by  these  thermometers.  It  can  be  seen  from  the 
graphical  log  that  the  temperatures  in  the  middle  of  the  rooms 
averaged  more  than  two  degrees  lower  than  the  temperatures 
near  the  inside  walls  during  the  time  the  fan  was  not  in  opera- 
tion. These  temperatures  became  nearly  equal  shortly  after  the 
fan  had  started. 


Tests  on  the  Recirculation  of  Washed  Air 


21 


In  the  two  tests  just  described  the  fan  was  operated  only  during 
the  time  that  the  building  was  full  of  students.  To  eliminate  the 
possibility  that  the  decrease  in  steam  consumption  resulted 
from  the  animal  heat  of  the  students,  a third  test  was  run  at  a 
time  when  the  building  was  unoccupied. 

This  test,  No.  3,  was  started  at  8 :15  P.  M.,  March  3rd,  and  con- 
tinued to  11  :15  P.  M.,  March  4th.  The  outside,  weather  condi- 
tions were  almost  an  exact  duplicate  of  the  conditions  when 
Test  No.  1 was  made.  The  average  outside  temperature  ranged 
from  23.6°  to  31.8°  with  a mean  of  27°.  The  average  inside  tem- 
perature for  the  run  was  65.3°  and  the  average  steam  consump- 
tion per  degree  difference  per  hour  was  22.1.  The  fan  was  started 
at  midnight  and  stopped  the  following  .evening  at  8:15  P.  M. 
No  definite  decrease  in  steam  consumption  is  shown  by  the  curves 
when  the  fan  was  started  but  they  do  show  a decided  increase 
immediately  after  the  fan  was  stopped. 

All  three  tests  show  a decided  decrease  in  steam  consumption 
during  the  time  the  fan  was  in  operation.  Test  No.  3 shows 
more  than  Test  No.  2 but  not  as  much  as  Test  No.  1.  For  the 
exact  percentages  see  the  chapter  on  “Calculations.”  . 

HUMIDITY  TESTS 

All  humidity  measurements  in  the  various  rooms  were  made 
with  a sling  psychrometer  of  the  pattern  recommended  by  the 
U.  S.  Weather  Bureau.  The  humidity  tests  made  on  the  air 
entering  and  leaving  the  washer  were  made  with  a Hygrodeik 
which  had  been  checked  with  the  sling  psychrometer. 

The  relative  humidity  in  the  various  rooms  as  shown  in  Table  I 
was  taken  on  one  of  the  coldest  days  in  the  winter.  It  varied 
greatly  in  the  various  rooms  but  the  average  for  the  entire  build- 
ing was  44%.  The  humidity  of  the  air  as  it  enters  the  washer 
can  be  taken  as  the  average  humidity  of  all  the  rooms.  That 
this  assumption  is  correct  is  shown  by  the  following  measure- 
ments taken  in  some  of  the  rooms  on  the  day  steam  consumption 
Test  No.  1 was  made. 


Room  Number 

Wet  Bulb 

Dry  Bulb 

Humidity 

Gymnasium 

58.3 

63.5 

74 

Room  No.  10 

54.5 

65 

50 

Room  No.  108 

59 

69 

55 

Room  No.  209 

59 

65 

70 

Assembly 

61.7 

69 

66 

Room  No.  309 

55.5 

66 

51 

Room  No.  311 

57.5 

64.5 

66 

Room  No.  211 

60 

69 

59 

Room  No.  107 

58.5 

67 

60 

Average 

28.2 

66.4 

61.2 

22 


Tests  on  the  Recirculation  of  Washed  Air 


The  average  humidity  of  all  the  above  rooms  was  61.2%  as 
compared  with  61.6%  in  the  air  entering  the  washer.  In  Test 
No.  2 the  average  humidity  of  the  air  entering  the  washer  was 
58.5%,  and  in  Test  No.  3 it  was  61.5%.  In  each  case  the  air  had 
a relative  humidity  of  about  95%  as  it  left  the  washer. 

There  can  be  no  doubt  but  that  a reasonably  high  humidity  has 
a very  beneficial  effect  upon  the  quality  of  the  air.  It  not  only 
improves  the  quality  of  the  air  for  breathing  but  it  makes  it  pos- 
sible to  keep  the  rooms  at  a muqh  lower  temperature.  An  inspec- 
tion of  any  of  the  temperature  log  sheets  will  show  that  the 
average  temperature  was  rarely  above  67°,  and  often  it  was  below 
65°  in  some  of  the  rooms,  without  a single  complaint  being  regis- 
tered. 

The  temperature  of  the  air  leaving  the  washer  was  usually 
about  60°.  A series  of  temperature  measurements  taken  in  the 
registers  of  the  various  rooms  showed  that  the  air  entering  the 
rooms  was  also  60°.  At  first  glance  one  would  say  that  this  was 
too  cold.  As  a matter  of  fact  it  proved  to  be  a benefit  rather 
than  a detriment,  as  it  seemed  to  give  more  life  to  the  air  in  the 
rooms  and  at  the  same  time  did  not  cause  any  uncomfortable 
draughts  as  would  be  expected. 

This  test  was  made  on  March  30th,  when  the  weather  was 
quite  mild.  ’No  test  has  been  made  during  the  summer  so  that  the 
writer  is  unable  to  state  what  entering  temperature  might  be 
expected  if  recirculation  is  resorted  to  during  the  summer  months. 
However,  in  view  of  the  fact  that  the  air  entered  at  60°  on  a 
comparatively  mild  day,  it  is  not  likely  that  the  temperature 
would  reach  an  unreasonable  value  during  the  warmer  months. 

CARBON  DIOXIDE  TESTS 

The  following  carbon  dioxide  tests  were  made  on  the  two 
sides  of  the  washer  and  in  the  various  rooms  mentioned. 

Tests  on  air  entering  washer  December  14th.  3:20  P.  M. : 

Sample  No.  1 showed  11  parts  carbon  dioxide  in  10,000. 

Sample  No.  2 showed  10  parts  carbon  dioxide  in  10,000. 
Tests  on  air  leaving  washer  December  14th.  3:35  P.  M. 

Sample  No.  1 showed  6 parts  carbon  dioxide  in  10,000. 

Sample  No.  2 showed  6 parts  carbon  dioxide  in  10,000. 

The  tests  tabulated  below  were  made  December  16th. 

TESTS  ON  AIR  ENTERING  THE  WASHER 


Time  10:45  10:55  11:01  2:45  2:56  Average 

Parts  in  10,000 8 6 8 10  10  8.4 


Tests  on  the  Recirculation  of  Washed  Air 


23 


TESTS  ON  AIR  LEAVING  TIIE  WASHER 

Time  10:15  11:20  11:30  11:42  11:53  2:15  2:30  Average 

Parts  in  10,000  10  9 7 8 0 8 6 8.14 

On  January  12th  the  following  results  were  obtained: 

Sample  No.  1 taken  9 :55  A.  M.  on  the  air  after  being  washed 
showed  6 parts  in  10,000. 

Sample  No.  2 taken  10:05  A.  M.  on  the  air  after  being  washed 
showed  7 parts  in  10,000. 

Sample  No.  3 taken  10  :25  A.  M.  on  the  air  before  being  washed 
showed  9 parts  in  10,000. 

Sample  No.  4 taken  10  :40  A.  M.  on  the  air  before  being  washed 
showed  9 parts  in  10,000. 

Sample  No.  5 taken  10  :53  A.  M.  on  the  air  before  being  washed 
showed  8 parts  in  10,000. 

An  average  of  the  above  set  of  readings  given  6.5  parts  in 
10,000  after  washing  and  8.66  parts  in  10,000  before  washing. 

The  above  tests  lead  to  the  conclusion  that  the  washer  water 
absorbs  a part  of  the  carbon  dioxide  brought  from  the  rooms  by 
the  air.  It  is  impossible  to  say  just  what  this  rate  of  absorption 
is  as  the  results  varied  considerably  and  the  readings  were  not 
taken  on  the  two  sides  of  the  washer  at  exactly  the  same  time. 
More  work  needs  to  be  done  along  this  line. 

Tests  were  also  made  on  the  air  in  some  of  the  rooms.  In 
room  No.  311  a sample  was  taken  while  the  class  was  in  the 
room  and  it  contained  15  parts  of  carbon  dioxide  while  a sample 
taken  seven  minutes  after  the  class  had  left  the  room  showed  13 
parts  of  carbon  dioxide  in  10,000. 

On  February  26th  samples  were  taken  in  room  No.  211  while 
19  students  were  in  the  room.  The  first  sample  showed  15  parts, 
the  second  13  parts,  and  the  third  13  parts  of  carbon  dioxide  in 
10,000.  These  tests  were  made  in  the  afternoon,  the  room  having 
been  in  use  all  day. 

On  this  same  day  samples  were  also  taken  in  the  auditorium 
near  the  close  of  an  assembly  period,  and  while  there  were  250 
students  in  the  room.  The  three  samples  taken  showed  15,  20  and 
17  parts  of  carbon  dioxide,  respectively. 

The  carbon  dioxide  content  shown  by  the  above  tests  is  con- 
siderably higher  than  would  be  considered  good  practice  accord- 
ing to  the  old  standard  of  6 parts  in  10,000,  but  it  is  lower  than 
would  be  expected  in  view  of  the  fact  that  all  the  air  is  recircu- 
lated and  none  is  taken  from  the  outside  except  the  usual  unavoid- 
able leakage.  As  far  as  could  be  detected  the  above  amounts 


24 


Tests  on  the  Recirculation  of  Washed  Air 


of  carbon  dioxide  had  no  detrimental  effect  upon  the  quality  of 
the  air  in  the  rooms.  The  air  seemed  fresh  and  clean  and  no 
odors  were  detected. 

THE  AIR  WASHER  AS  A DUST  REMOVER 

No  actual  dust  counts  were  taken  on  the  washer  but  it  was 
readily  seen  that  it  was  quite  efficient  in  this  respect.  At  the 
end  of  a week’s  run  the  washer  water  was  found  to  be  very  dirty 
and  considerable  sediment  was  found  on  the  bottom  of  the  tank. 
However,  the  writer  doubts  very  much  the  claims  made  by  most 
washer  manufacturers  to  the  effect  that  their  washers  will  remove 
98%  of  the  solid  matter  in  the  air. 

BACTERIA  TESTS 

These  tests  showed  some  startling  and  unexpected  results. 
When  using*  recirculated  water  the  washer  supplied  bacteria  to 
the  air  instead  of  removing  them  and  even  when  using  new  water 
continuously  it  did  not  show  any  marked  efficiency  as  a bacteria 
remover.  These  results  are  directly  contrary  to  the  results  re- 
ported by  G.  C.  Whipple  and  M.  C.  Whipple  of  Harvard.  (See 
the  American  Journal  of  Public  Health,  1913,  Vol.  23,  pp.  1138- 
1153.) 

The  tabulated  results  of  the  tests  are  given  in  the  following 
tables : Table  V shows  the  results  obtained  with  the  use  of  sand 
and  sugar  filters.  No  conclusive  results  were  obtained  using- 
sugar  filters,  probably  due  to  the  trouble  mentioned  previously 
in  the  description  of  the  apparatus.  On  an  average,  the  sugar 
filters  showed  about  the  same  number  of  bacteria  on  each  side 
of  the  washer  but  the  highest  number  would  appear  on  one  side 
of  the  washer  in  one  test  and  on  the  opposite  side  in  the  next. 

The  sand  filters  showed  conclusively  that  the  washer  delivered 
bacteria  to  the  air.  The  four  sand  filter  tests  checked  each  other 
very  closely  and  showed  an  increase  of  bacteria  in  a ratio  of 
about  two  to  one.  At  the  same  time  that  the  sand  filter  tests 
were  taken,  a series  of  Petrie  plates  were  exposed  for  the  same 
length  ©f  time  on  each  side  of  the  washer.  These  also  show 
conclusively  that  the  number  of  bacteria  in  the  air  is  increased 
by  the  washer,  but  at  a very  much  higher  ratio  than  shown  by 
the  sand  filters.  The  results  of  the  tests  with  Petrie  dishes  are 
tabulated  in  Table  VI.  Figure  VII  is  a plan  of  the  washer  and 
fan  housing  showing  where  the  bacteria  plates  were  exposed.  The 
writer  is  unable  to  state  just  why  the  plates  should  show  such  a 
greater  ratio  above  that  shown  by  the  sand  filters.  It  can  not  be 


6-0 


Tests  on  the  Recirculation  of  Washed  Air 


25 


26 


Tests,  on  the  Recirculation  of  Washed.  Air 


Table  V 

Bactebia  Tests  on  Air  Washeb 

All  samples  taken  with  Sugar  Filtegs 
andSand  Filters 


fc 

IL 

0 

& 

UJ  UJ 

Air  before  Washing 

Air  after  Washing 

< 

IL 

0 

111 

5 

F 

O 

“z 

Si 

F 

< Z 
iu  8 

r 

u < 

< 0 

<| 

K 

F 2 

10  S 

10 

0 

_J 

8 

z 

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2i-° 

to5 

P<o 

h<05 

| 

0 

IU 

2 

F 

0 

S 10 
5 Si 
8$ 
z * 
F 

jl 

SI 

« V 
S I 

0 Z 

< 5 

8 

8 

z 

TOTAL. 

BACTERIA 

and  Moulds 

JAN.  5 

s 

3:00-3.10 

IO- 

42 

42 

240-250 

10 

4 

4 

JAN.© 

s 

303-3:20 

11 

4 

4 

241-254 

13 

3 

3 

JAN  .7 

s 

Z40-ZS3 

13 

1 

1 

3:os-3:i3 

8 

O 

O 

JAN.S 

s 

315-323 

a 

7 

7 

257-305 

8 

1 

1 

JAN.ll 

IO 

230-3W 

36 

4 

4 

314-330 

16 

0 

O 

JAN.lE 

IO 

2:55*3.09 

14- 

1 

J 

232-2.43 

O 

0 

JAN.I3 

IO 

2:35-E:53 

16 

O 

O 

304-315 

11 

O 

0 

t 

1 

3 

II 

o 

JAN.  14 

IO 

3.12-  334 

22 

5 

S 

240- 3P3 

23 

3 

3 

{ 

> 

D 

Jan.  is 

IO 

2:06-2144 

33 

O 

.O  . 

232-337 

4S 

3 

3 

t 

l 

u 

Jan2S 

IO 

230-252 

22 

25 

2 

27 

230-252 

22 

2 

0 

2 

r 

J 

JAN.26 

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23 

21 

1 

22 

248-3: 1 1 

23 

11 

0 

11 

1 

V 

JAN.27 

IO 

232-228 

56 

12 

II 

23 

232-32  3 

51 

20 

0 

20 

( 

( 

5 

JAN28 

'? 

223-3:« 

50 

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50 

2o 

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J 

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JAN?9 

IO 

2:30-3is 

45 

25 

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29 

230-315 

4S 

IO 

0 

10 

FEB.  1 

1° 

2:43213 

36 

25 

O 

2S 

243-319 

36 

33 

0 

39 

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IO 

2:30-205 

3S 

IO 

O 

10 

230-305 

35 

40 

0 

40 

FE&3 

IO 

CS4-22S 

31 

4S 

O 

4S 

1:542.25 

31 

198 

2 

Zoo 

FEB.  4 

IO 

242-225 

43 

6 

2 

6 

242-325 

43 

16 

1 

17 

V) 

Qi 

Feb.8 

IO 

3.00- 32S 

25 

30 

2 

32 

3:00  325 

25 

70 

4 

74 

FEB.3 

IO 

235300 

2£ 

33 

O 

33 

23S-300 

25 

60 

2 

62 

0 

z 

2 

FEB-'O 

IO 

255320 

23 

31 

1 

32 

255-320 

25 

57 

2 

59 

< 

FEB.I  1 

IO 

245310 

25 

36 

0 

36 

245-310 

25 

66 

O 

66 

mote 

T ME  SAMPLE  OF  THE  AIR  BEFORE  WASHING  ON  JANUARY  5-  WAS 

taken  directly  in  front  of  the  washer  and  evidently  water  from 
the  washer  splashed  into  the  filter  tube.  All  other  samples 

OF  THE  AIR  BEFORE  WASHING  WERE  TAKEN  IN  THE  RETURN  DUCTS  WHERE 
IT  WAS  IMPOSSIBLE  FOR  THE  WASHER  WATER  TO  REACH  THEM. 

The  washer  water  was  changed  weekly. 

wholly  explained  from  the  different  air  velocities  on  the  two  sides 
of  the  washer.  The  average  velocity  of  the  air  entering  the  fan 
was  940  feet  per  minute.  The  average  velocity  on  the  other  side 
of  the  washer  was  564  feet  per  minute  in  the  north  duct  and  813 
feet  per  minute  in  the  south  duct,  and  it  can  be  easily  seen  that 
this  will  not  account  for  all  of  the  difference. 

The  tests  show  no  appreciable  decrease  in  bacteria  due  to  the 
washer  water  being  changed  each  Monday.  Evidently  the  wash- 
er walls  were  covered  with  bacteria  from  the  water  used  the 
previous  week  and  hence  the  high  count  at  the  beginning  of  the 
following  week.  After  March  16th  fresh  water  was  used  con- 
tinuously in  the  washer  and  tests  were  again  taken  March  25th 
and  April  1st.  These  tests  show  an  enormous  decrease  in  the 
number  of  bacteria  leaving  the  washer,  but  still  most  of  the 
bacteria  which  came  to  the  washer  went  through  it. 


Tests  on  the  Recirculation  of  Washed  Air 


27 


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28 


Tests  on  the  Recirculation  of  Washed  Air 


After  April  1st  the  water  was  changed  daily  and  tests  under 
these  conditions  were  made  on  April  16th  and  April  23rd.  The 
results  show  no  advantage  in  changing  the  water  daily  as  the 
number  of  bacteria  leaving  the  washer  is  almost  as  great  as  when 
the  water  was  only  changed  weekly. 

As  a check  upon  the  above  results,  Petrie  plates  were  also  ex- 
posed at  the  inlet  and  outlet  registers  of  some  of  the  rooms. 
Table  VIII  is  a tabulation  of  these  results.  All  of  them  show 
more  bacteria  coming  into  the  rooms  than  going  out. 

Bacteria  tests  were  also  taken  on  the  washer  water.  Table  VII 
shows  the  multiplication  of  bacteria  in  the  water  when  it  is  recir- 
culated for  a week  and  Figure  VIII  shows  the  same  in  the  form 
of  a curve. 

Table  IX  shows  the  results  of  plates  exposed  to  the  outside  air. 
These  were  taken  in  comparatively  still  air  and,  when  comparing 
them  with  the  plates  exposed  in  the  ducts,  the  air  velocity  should 
be  taken  into  consideration. 


Tests  on  the  Recirculation  of  Washed  Air 


29 


Fig.  x. 


+ 3 


Fig.  IX. 


30 


Tests  on  the  Recirculation  of  Washed  Air 


Figure  IX  is  a photograph  of  two  of  the  plates  taken  when  the 
washer  water  was  being  recirculated  for  a week.  No.  2 was 
exposed  to  the  air  after  it  had  passed  through  the  washer,  and 
No.  3 was  exposed  to  the  air  before  it  had  passed  through  the 
washer. 

Figure  X is  a photograph  of  three  plates  taken  after  fresh 
water  had  been  used  continuously  for  ten  days  in  the  washer. 
No.  4 was  exposed  to  the  outside  air.  No.  5 was  exposed  to  the 
air  after  it  had  passed  through  the  washer,  and  No.  6 was  ex- 
posed to  the  air  before  it  had  passed  through  the  washer.  All 
three  were  thirty  minute  exposures. 

Figure  XI  is  a photograph  of  three  plates  exposed  after  the 
washer  water  had  been  changed  daily  for  ten  days.  No.  7 was 


Tests  on  the  Recirculation  of  Washed  Air 


31 


exposed  to  the  air  before  it  had  passed  through  the  washer. 
No.  8 was  exposed  to  the  air  after  it  had  passed  through  the 
washer,  and  No.  9 was  exposed  to  the  outdoor  air  for  the  same 
length  of  time. 

CALCULATIONS 

CALCULATION  OF  WATER  EVAPORATED  IN  WASHER 

The  figures  used  below  are  average  values  from  a six  hour 
test  that  was  made  to  ascertain  the  amount  of  water  used  by  the 
washer. 

North  Duct:  Temperature  of  air  69.5°.  Humidity  78%.  The 
weight  of  water  vapor  per  cubic  foot  at  69.5°  and  78%  humidity 
is  6.1252  grains. 

South  Duct:  Temperature  of  air  70.3°.  Humidity  72%.  The 
weight  of  water  vapor  per  cubic  foot  at  70.3°  and  72%  humidity 
is  5.801  grains. 


AFTER  WASHING 

Temperature  of  air  65°.  Humidity  98%.  The  weight  of  water 
vapor  per  cubic  foot  at  65°  and  98%  humidity  is  6.6466  grains. 

The  weight  of  water  vapor  gained  by  air  from  North  Duct  is 
6.6466  — 6.1252  = 0.5214  grains  per  cubic  foot. 

The  weight  of  water  vapor  gained  by  air  from  South  Duct  is 
6.6466  — 5.801  — 0.8456  grains  per  cubic  foot. 

Cubic  feet  of  air  per  minute  passing  through  the  North  Duct 
is  5,780, 

Cubic  feet  of  air  per  minute  passing  through  the  South  Duct  is 
8,340. 

Total  weight  of  water  gained  by  air  from  North  Duct  — 

5780  x 60x0.5214 

7000  x 8.3356  = 3J  galIonS  per  h°Ur' 

Total  weight  of  water  gained  by  air  from  South  Duct  = 

>7000  x 8.335'6~~A 

8340x60  x 0.8456>  7-25  gaU°nS  p6r  h°Un 

Total  weight  of  water  given  to  air  by  washer  under  above  con- 
ditions of  temperature  and  humidity  = 3.1  -f-  7.25  — 10.35  gal- 
lons per  hour. 

The  washer  tank  dimensions  are  8'  x 5'  x 1.25'.  It  was  found 
by  measurement  that  the  water  level  decreased  two  inches  in  six 
hours,  the  make  up  water  being  shut  off.  Therefore  by  actual 
measurement  the  water  given  to  the  air  by  the  washer  under  the 
above  conditions  was  8 x 5 x 2/12  x 7.5  = 8.34  gallons  per  hour. 


Tests  on  the  Recirculation  of  Washed  Air 


The  discrepancy  between  the  pounds  of  water  actually  meas- 
ured and  the  pounds  of  water  calculated  from  the  humidity  tables 
is  probably  due  to  the  inaccuracy  of  humidity  measurement. 

The  weight  of  washer  water  was  obtained  at  the  same  time  the 
above  humidity  measurements  were  taken.  From  these  figures 
an  interesting  check  on  the  volume  of  air  passing  through  the 
washer  can  be  made. 

The.  average  temperature  drop  in  the  air  going  through  the 
washer  was  4.9  degrees  and  the  weight  evaporated  was  8.34  gal- 
lons per  hour. 

8.34  x 8.3356  = 69.52  pounds  per  hour. 

The  temperature  of  the  washer  water  was  64  degrees  and  the 
latent  heat  of  vaporization  at  64  degrees  is  1,056  B.  t.  u. 

The  volume  of  air  which  will  be  cooled  4.9  degrees  by  the  evap- 
oration of  69.52  pounds  of  water  is  approximately 
69.52  x 55  x 1056 

, - — = 13,750  cubic  feet  per  minute. 

4.9  x 60 

COST  OF  WATER  FOR  AIR  WASHING 

To  get  the  cost  of  air  washing  it  is  assumed  that  the  cost  of 
water  is  five  cents  per  thousand  gallons,  as  estimated  by  Mr. 
J.  M.  Smith  from  his  cost  data  of  operating  University  pumping 
plant,  and  that  the  washer  is  in  service  eight  hours  a day  and 
five  days  a week.  It  is  also  assumed  that,  under  the  average  run- 
ning conditions,  the  air  passing  through  the  washer  absorbs  ten 
gallons  of  water  per  hour  and  that  the  tank  is  filled  to  a depth  of 
ten  inches  each  time  a change  of  water  is  made. 

Make  up  water  is  admitted  to  the  tank  by  a float  valve. 
Condition  No.  1 : 

Washer  water  recirculated  for  a week,  beginning  with  fresh 
water  each  Monday  morning. 

Cost  of  water  per  week, 

10  .05 

[8  x 5 x — x 7.5  + 10  x 8 x 5]  x = $0.0325 

12  1000 

Condition  No.  2 : 

Washer  water  recirculated  for  8 hours  beginning  with  fresh 
water  each  morning. 

Cost  of  water  per  week, 

10  .05 

[ (8  x 5 x — x 7.5)  x5  -f  10x8x5]  x 

12  1000 


= $0.0825. 


Tests  on  the  Recirculation  of  Washed  Air 


33 


Condition  No.  3: 

Fresh  water  used  continuously.  Under  conditions  No.  1 and 
No.  2 the  water  pressure  on  the  spray  nozzles  averaged  about  12 
pounds  per  square  inch  gage. 

With  12  pounds  pressure  on  the  spray  nozzles,  measurements 
were  taken  to  ascertain  the  cost  of  using  fresh  water  continu- 
ously. With  the  drain  from  the  tank  closed  it  was  found  that  it 
required  two  minutes  for  the  water  in  the  tank  to  rise  eleven 
inches. 

Therefore  the  fresh  water  required  when  used  continuously 
would  be 
5.5 

8 x 5 x x 60  x 7.5  = 8250  gallons  per  hour 

12 

Cost  of  water  per  week, 

.05 

8250  x 8 x 5 x = $16.50 

1000 

COST  OF.  POWER  FOR  RECIRCULATING  WASHER  WATER 

The  average  power  required  to  drive  the  centrifugal  pump  was 

2.41  K.  W. 

The  cost  of  this  power  for  a week  would  be 

2.41  x 8 x 5 x .025  — $2.41 

The  total  cost  of  running  the  washer  then  is 

2.41  .0325  = $2.4425  for  Condition  No.  1. 

2.41  + .0825  = $2.4925  for  Condition  No.  2. 
and  $16.50  for  Condition  No.  3. 

CALCULATION  OF  THE  ECONOMY  OF  RECIRCULATION  OF  AIR 

In  each  of  the  runs  made  the  air  leaving  the  washer  and  enter- 
ing the  rooms  was  at  an  average  temperature  of  about  60°.  The 
average  outside  temperature  during  the  time  the  fan  was  running 
was  25.4°,  30.5°  and  27°  respectively  for  the  first,  second  and 
third  tests.  The  total  amount  of  air  delivered  to  the  rooms  in 
each  case  was  approximately  15,000  cubic  feet  per  minute.  If  this 
air  had  been  taken  from  the  outside  instead  of  being  recirculated, 
the  additional  steam  required  would  have  been 
60  x 15000 

— — — „ ^ x (60  — 25.4)  = 590  pounds  per  hour  for  the  first  test. 
55  x 960 

The  above  calculation  is  based  on  the  following  figures : 


34 


Tests  on  the  Recirculation  of  Washed  Air 


The  average  steam  pressure  on  the  building  during  all  three 
tests  was  5.3  pounds  gage  and  the  average  temperature  of  the 
condensed  steam  leaving  the  building  was  209°.  The  quality  of 
the  steam  entering  the  building  averaged  98%.  Therefore  each 
pound  of  steam  gave  up  .98  x 960  + 196.1  — (209  — 32)  = 960'  B. 
t.u.  It  is  assumed  that  one  B.t.u.  will  raise  55  cubic  feet  of  air 
one  degree  of  temperature. 

The  additional  steam  required  for  the  second  test  would  have 
, 60x  15000 

been  ^ — x (60  — 30.5)  = 503  pounds  per  hour  and  for  the 

third  test 
60 x 15000 

x (60  — 27)  = 562  pounds  per  hour. 

00  X J6U 

The  actual  weight  of  steam  used  by  the  building  during  the 
time  the  fan  was  running  was  834.6,  573.1  and  824  pounds  per 
hour  for  the  first,  second  and  third  tests,  respectively. 

The  percentage  of  steam  saved  by  recirculation  of  air  in  each 
590 

case  is 


590  + 834.6 


& 41.4%  for  the  first  test. 


503 


503  + 573.1 
562 

and 


46.5%  for  the  second  test. 

= 40.5%  for  the  third  test. 


562  + 824 

Since  the  fan  in  actual  practice  is  only  operated  8 hours  out  of 
24,  the  saving  from  recirculation  will  not  be  as  much  as  shown 
above. 

Running  the  fan  8 hours  the  saving  for  the  entire  24  hour  period 
8 x 590 

will  be  ---■  — - — — - — 16.8%  from  the  first  test  and 

8 x 590  % 23161 

8x503 

19.2%  from  Test  No.  2. 


8 x 503  + 16988 


THE  EFFECT  OF  THE  FAN  UPON  THE  STEAM  CONSUMPTION 


TEST  NO.  I 

February  2nd  and  3rd 

The  total  weight  of  steam  used  by  radiators  when  the  fan  was 
in  operation  was  6676.5  pounds,  or  an  average  of  834.6  pounds 
per  hour  for  8 hours.  Total  weight  of  steam  used  when  the  fan 
was  not  in  operation  was  16483.5  pounds,  or  an  average  of  1030.2 
pounds  per  hour  for  16  hours.  The  difference  in  average  steam 


Tests  on  the  Recirculation  of  Washed  Air 


35 


consumption  is  1030.2  — 834.6  = 196.2  pounds  per  hour  in  favor 
of  the  fan. 

Since  some  of  the  above  saving  may  be  due  to  unequal  outside 
temperatures  during  the  two  parts  of  the  run,  it  is  best  to  base 
the  relative  performance  on  the  basis  of  per  degree  difference  of 
temperature. 

Average  pounds  of  steam  per  hour  per  degree  difference  of  tem- 
perature while  fan  was  in  operation  is  19.8  pounds. 

Average  pounds  of  steam  per  degree  difference  of  temperature 
per  hour  during  time  when  fan  was  not  in  operation  is  26.64 

6.84 

pounds.  The  difference  is  6.84  pounds,  or  a saving  of  = 

2o.ol 

25.7%  in  favor  of  running  the  fan. 

TEST  NO.  II 

February  27th  and  28th 

Total  weight  of  steam  used  by  radiators  during  the  time  the 
fan  was  in  operation  was  4,585  pounds,  or  an  average  of  573.1 
pounds  per  hour  for  eight  hours.  The  total  weight  of  steam  used 
during  the  time  the  fan  was  not  in  operation  was  12,403  pounds 
or  an  average  of  775  pounds  per  hour  for  sixteen  hours.  The 
difference  in  average  steam  consumption  is  201.9  pounds  per 
hour. 

Average  pounds  of  steam  per  hour  per  degree  difference  of 
temperature  during  time  that  fan  was  in  operation  = 16.18 
pounds. 

Average  pounds  of  steam  per  degree  difference  per  hour  dur- 
ing time  the  fan  was  not  in  operation  — 17.66  pounds. 

1.48 

The  difference  is  1.48  pounds,  or  a saving  of  ^ ^ ■=  8.38% 
in  favor  of  running  the  fan. 

TEST  NO.  Ill 

March  3rd  and  4th 

Total  weight  of  steam  used  by  radiators  during  the  time  the 
fan  was  in  operation  was  16,485  pounds,  or  an  average  of  824.2 
pounds  for  twenty  hours.  Total  weight  of  steam  used  by  the 
radiators  during  the  time  the  fan  was  not  in  operation  was  6,369 
pounds,  or  an  average  of  910'  pounds  per  hour  for  seven  hours. 

Difference  in  average  steam  consumption  — 86  pounds  per 
hour. 


36 


Tests  on  the  Recirculation  of  Washed  Air 


Pounds  of  steam  per  hour  per  degree  difference  during  time 
the  fan  was  in  operation  = 21.54. 

Pounds  of  steam  per  hour  per  degree  difference  during  the 
time  the  fan  was  not  in  operation  = 23.81. 

2.27 

The  difference  is  2.27  pounds,  or  a saving  of  —--—=9.53% 

io  . 81 

in  favor  of  running  the  fan. 

A COMPARISON  OF  THE  SAVING  MADE  BY  KEEPING  THE  AIR  IN  MOTION 
AND  THE  COST  OF  OPERATING  THE  FAN 

Will  it  pay  to  operate  the  fan  continuously?  To  answer  this 
question  the  following  calculations  have  been  made : 

The  cost  of  steam  delivered  to  the  building  is  approximately 
27c  per  thousand  pounds  and  the  cost  of  power  is  approximately 
2*/2C  per  kilowatt  hour. 

According  to  the  figure  obtained  from  the  first  test  a saving  of 
25.7%  in  steam  consumption  was  made  by  running  the  fan  to 
keep  the  air  in  motion.  The  total  pounds  of  steam  used  during 
the  sixteen  hours  that  the  fan  was  standing  idle  was  16,483.5 
pounds.  Had  the  fan  been  running  during  this  period  a saving  of 
16,483.5  x .257  or  4,235  pounds  of  steam  would  have  been  obtained. 

4235 

Cost  of  steam  saved  ~ ^qqq~  x = $1-144. 

516  x 7.85 

Cost  of  operating  the  fan  = fqoo — x 16  x .025  = $1.62. 

The  saving  in  the  second  test  would  have  been  12403  x .0838.  or 
1040  pounds  of  steam. 

1010 

Cost  of  steam  saved  - x 0.27 

/ToooN 

Cost  of  operating  the  fan  - — Ax  16  x .025  = $1,656. 

(51o  X oj 

The  volts  and  amperes  used  in  the  above  calculations  are  aver- 
age values  of  the  power  consumption  of  the  fan  motor. 

The  third  test  would  show  about  the  same  relative  cost  as  the 
second  test. 

The  second  and  third  tests  probably  give  the  fairest  idea  of  the 
saving  of  steam  obtained  by  keeping  the  air  in  motion.  Obviously 
the  cost  of  power  for  the  fan  more  than  overcomes  the  saving 
resulting  from  its  use. 

In  all  of  the  tests  the  air  temperature  was  reduced  about  six 
degrees  in  passing  through  the  washer.  If  the  washer  had  been 


: $0.28 


Tests  on  the  Recirculation  of  Washed  Air 


37 


shut  down  during  the  time  there  were  no  students  in  the  building, 
a greater  saving  of  steam  would  have  resulted  from  keeping  the 
air  in  motion.  But  even  under  such  conditions,  the  saving  would 
not  have  been  enough  to  overbalance  the  cost  of  power  for  the 
fan. 

Take  Test  No.  2 for  comparison.  In  this  test  the  saving  that 
would  result  from  running  the  fan  and  washer  for  the  additional 
sixteen  hours  was  shown  to  be  1040  pounds  of  steam.  The  drop 
of  temperature  in  the  washer  was  six  degrees  and  the  air  passing 
through  it  was  15,000  cubic  feet  per  minute.  The  extra  steam  con- 
sumption required  to  replace  the  heat  taken  away  by  the 
of  1631  pounds-  for  the  "sixteen  hours.* 

6 x 15000  x 60 

washer  water  was  — — — —7 r — £=  102  pounds  per  hour,  or  a total 
55  x 960 

of  1635  pounds  for  the  sixteen  hours. 

Therefore,  with  the  fan  running  and  the  washer  cut  out,  the 
total  saving  of  steam  would  have  been  1040  1635,  or  2675 

2675 

pounds.  The  cost  of  this  steam  would  be  ■-  x 0.27  = $0.72  as 

compared  with  $1,656  for  power  to  run  the  fan. 

The  steam  cost  used  in  the  above  calculations  is  below  the  aver- 
age and  there  may  be  conditions  where  high  steam  cost  and  low 
power  cost  will  justify  the  running  of  the  fan  continuously. 

Lack  of  time  made  it  impossible  to  check  these  last  calculations 
with  an  actual  test  of  steam  consumption  for  recirculated  air  with 
the  washer  cut  out.  It  would  be  interesting  to  see  how  it  would 
work  out  in  actual  practice. 


STEAM  USED  PER  SQUARE  FOOT  OF  RADIATION  PER  HOUR 


The  steam  consumed  by  the  radiators  per  square  foot  of  radia- 

23161 


tion  per  hour  in  the  first  test  was 


24  x 8530 


— ■ — 0.113  pounds 


16988 
24  x 8530 


= 0.083  pounds  for  the  second  test 


22854 

and  — = 0.0993  for  the  third  test. 

/v  i X 0O0U 

The  average  for  the  three  tests  is  .0984,  or  approximately 
l/10th  of  a pound  of  steam  per  square  foot  of  radiation  per  hour. 

Since  an  average  radiator  will  condense  l/4th  of  a pound  of 
steam  per  square  foot  per  hour  under  extreme  conditions  the  re- 
sults show  that  the  building  has  ample  radiating  surface  for  any 
conditions  which  may  arise. 


38 


Tests  on  the  Recirculation  of  Washed  Air 


TOTAL  COST  OF  HEATING  AND  VENTILATING  THE  BUILDING  FOR  A 
TYPICAL  DAY  OF  24  HOURS 
Data  taken  from  Test  No.  I 

.0325 

Cost  of  washer  water  = = $0.0065. 

5 

2.41 

Cost  of  power  for  washer  pump  =- — — — $0.48. 

_ 518x7.85 

Cost  of  power  for  ventilating  fan  = x 8 x .0252  — 

$0.81. 

Cost  of  steam  for  heating  = 23161  x .27  = $6,253. 

Total  cost  per  day  = $7.55. 

To  the  above  total  cost  should  be  added  the  cost  of  running 
the  two  small  exhaust  fans  in  the  attic. 

The  hot  water  tanks  were  cut  out  during  the  tests  so  that  no 
data  is  available  for  the  cost  of  steam  for  heating  water. 

The  recirculating  system  was  put  into  operation  at  the  be- 
ginning of  school,  September  1914,  and  was  in  operation  through- 
out the  whole  school  year.  The  principal  tests  were  made  in  the 
months  of  January,  February  and  March,  and  the  last  of  the  bac- 
teria tests  was  made  in  April. 

The  questionaire  was  submitted  to  the  teachers  on  May  13th  and 
the  reports  were  handed  in  by  them  about  three  days  later.  This 
was  about  two  weeks  before  school  closed,  the  teachers  having  had 
nine  months  to  form  their  conclusions  in  regard  to  the  system. 
An  interesting  point  in  regard  to  the  system  came  out  about  two 
weeks  ago  (Sept.  1915).  The  fan  motor  burned  out  and  it  took 
several  days  to  get  it  into  running  condition  again.  The  teach- 
ers were  not  aware  that  anything  had  happened  but  complaints 
soon  began  to  pour  in  that  there  was  something  wrong  with  the 
ventilation. 


QUESTIONAIRE  SUBMITTED  TO  TEACHERS 

A questionaire  was  submitted  to  the  various  teachers  in  the 
school  in  order  to  get  their  opinion  of  the  system  and  its  effect 
upon  the  students. 

The  questions  were  as  follows : 

1.  Has  your  room  been  sufficiently  heated? 

2.  Has  the  ventilation  been  satisfactory? 

3.  Has  the  air  in  the  room  been  too  moist  or  too  dry? 


Tests  on  the  Recirculation  of  Washed  Aii< 


39 


4.  lias  the  moisture  in  the  air  had  a good  or  bad  effect  upon 
the  quality  of  the  air  in  the  room? 

5.  If  the  moisture  has  had  a bad  effect  please  state  what  the 
effect  is. 

6.  Has  the  room  seemed  close? 

7.  Have  you  noticed  any  unpleasant  odors? 

8.  Have  the  students  been  bright  and  alert  or  (frowsy  and  list 
less? 

9.  How  does  the  ventilation  in  this  building  compare  with  that 
of  other  buildings  in  which  you  have  taught? 

10.  How  does  the  general  health  and  alertness  of  the  students 
in  this  building  compare  with  that  of  students  in  other  buildings 
in  which  you  have  taught? 

RESULTS  FROM  THE  QUESTION  AIRE 

Question  No.  1. 

All  of  the  fifteen  teachers  answered  “yes”. 

Question  No.  2. 

Twelve  teachers  answered  “yes.” 

Teacher  J answered  “nearly  so”,  Teacher  M,  “no”. 

Teacher  N,  “In  the  morning,  yes;  in  the  afternoon,  no”. 
Question  No.  3. 

Teacher  A — “Rarely  too  moist”. 

Teachers  B,  G,  I and  K— “No”. 

Teachers  C,  D and  H — “Neither”. 

Teacher  E — “If  anything,  too  moist  at  times”. 

Teacher  F— “Yes”. 

Teachers  J and  N — “A  little  dry”. 

Teachers  L,  M,  and  O — “Just  right”. 

Question  No.  4. 

Ten  teachers  answered  “Good”. 

Teacher  A — “Not  strictly  bad  at  any  time”. 

Teacher  B — “Apparently  good”. 

Teacher  F — “Did  not  notice.” 

Teacher  L — “Have  not  noticed  any  bad  effects”. 

Question  No.  5. 

No  statements  given  by  any  of  the  teachers. 

Question  No.  6. 

Teachers  A and  C — “Only  when  it  is  first  opened  in  the  morn- 
ing”. 

Teacher  B — “Very  seldom.” 

Teachers  D and  G — -“No”. 

Teacher  E — “No,  until  recently”. 


40 


Tests  on  the  Recirculation  of  Washed  Air 


Teacher  F — “Not  usually”. 

Teacher  H- — “In  warm  weather  if  windows  are  closed,  yes”. 
Teacher  I — “At  times  windows  have  had  to  be  opened”. 
Teacher  J— “A  little”. 

Teacher  K — “No,  except  in  the  morning  before  the  fan  had 
run  sufficiently”. 

Teacher  L — “Sometimes”. 

Teacher  M — “In  room  No.  115,  no ; in  room  No.  311,  yes”. 
Teacher  N— “Yes”. 

Teacher  O — “Not  often”. 

Question  No.  7. 

Twelve  teachers  answered  “no”. 

Teacher  M — “Room  No.  115,  no;  room  No.  311,  yes”. 

Teacher  N— “Yes”. 

Teacher  O — -“Seldom”. 

Question  No.  8. 

Six  teachers  answered  “Bright  and  alert”. 

Teacher  G — “Depends  more  on  students  than  on  room  condi- 
tions”. 

Teacher  H— “Neither,  some  of  each  in  each  class.” 

Teacher  I — “Not  drowsy  and  listless  as  a rule”. 

Teacher  J — “Both,  but  listlessness  not  due  to  ventilation”. 
Teacher  K — “We  have  both  kinds,  but  the  room  conditions  did 
not  make  them  so”. 

Teacher  L — “Attitude  varies”. 

Teacher  M — “Both”. 

Teacher  N — “Bright  in  morning;  drowsy  from  2:30-3:30 
P.  M”. 

Question  No.  9. 

Six  teachers  answered  “Better”. 

Teacher  A — “Infinitely  better”. 

Teacher  B — “Better  (have  taught  in  six  schools”). 

Teacher  C — “Most  favorably”. 

Teacher  D — “Best  in  my  experience”. 

Teacher  E— “There  is  much  more  moisture  in  the  air”. 
Teacher  K — “Excellent”. 

Teachers  M and  N — “Favorably”. 

Question  No.  10. 

Teachers  A and  G — “Better”. 

Teacher  B — “Much  better”. 

Teachers  C,  I and  L — “Favorably”. 

Teacher  D — “Have  not  noticed  health  especially.  Should  call 
alertness  better  than  usual  class”. 


Tests  on  the  Recirculation  of  Washed  Air 


41 


Teacher  E — “Have  no  data”. 

Teacher  F — “Don’t  know  of  any”. 

Teacher  H — “Not  so  alert  here,  health  better”. 

Teacher  K — “About  the  same,  perhaps  somewhat  better”. 

Teachers  M and  O — “About  the  same”. 

Teacher  N — “Better  than  elsewhere”. 

CONCLUSIONS 

1.  The  tests  show  that  it  is  both  unnecessary  and  uneconomic 
cal  to  supply  large  volumes  of  air  to  obtain  good  ventilation. 

2.  That  15  cubic  feet  per  student  would  be  ample  providing  it 
enters  the  room  at  a fairly  high  velocity  and  carries  the  proper 
amount  of  moisture. 

3.  With  humidity  ranging  from  50  to  70  per  cent.,  the  occu- 
pants of  the  rooms  are  perfectly  comfortable  at  a temperature  of 
65  degrees  or  even  less. 

4.  With  humidity  of  about  60  per  cent.,  the  air  can  enter  the 
rooms  at  a temperature  of  60  degrees  without  creating  any  dis- 
comfort ; in  fact  it  seems  to  give  life  to  the  air  and  aids  in  the 
efficiency  of  ventilation. 

5.  Carbon  dioxide  content  as  high  as  20  parts  in  10,000  does 
not  have  a bad  effect  upon  the  ventilation. 

6.  Ventilation  by  recirculation  is  both  efficient  and  economi- 
cal. At  the  end  of  a year’s  run  the  teachers  are  almost  unanimous 
in  their  praise  of  the  system. 

7.  With  a recirculating  system  such  as  this,  it  requires  from 
40  to  50  per  cent,  less  steam  to  heat  the  building  while  the  fan  is 
in  operation  than  would  be  required  if  the  air  was  drawn  from 
outdoors  for  the  same  length  of  time. 

8.  Air  movement  keeps  the  temperature  uniform  in  various 
parts  of  the  room  and  decreases  the  amount  of  steam  required  for 
heating.  The  tests  show  a minimum  saving  of  about  8 per  cent, 
due  to  this  air  movement  and  this  would  be  true  whether  the 
system  is  a recirculating  one  or  otherwise. 

9.  The  air  washer  absorbs  a considerable  amount  of  the  car- 
bon dioxide  contained  in  the  air  passing  through  it. 

10.  The  air  washer  is  apparently  quite  efficient  as  a dust  re- 
mover but  it  does  not  remove  bacteria  from  the  air  when  the 
washer  water  is  recirculated.  The  tests  show  that  it  actually 
supplies  bacteria  to  the  air  under  such  conditions. 

11.  In  spite  of  the  poor  showing  of  the  washer,  the  air  enter- 
ing the  rooms  carries  no  more  bacteria  than  outside  air  when  the 


42  Tests  on  the  Recirculation  of  Washed  Air 

relative  velocities  in  which  the  plates  were  exposed  is  taken  into 
account. 

The  writer  plans  to  continue  these  tests  this  coming  winter 
with  a view  of  ascertaining  the  effect  of  recirculation  upon  the 
oxygen  content  of  the  air.  Further  tests  will  also  be  made  to 
determine  more  accurately  the  amount  of  carbon  dioxide  absorbed 
by  the  washer,  and  experiments  will  be  carried  on  with  various 
methods  of  eliminating  bacteria  from  the  washer  water. 

ADDENDUM* 

A few  words  of  explanation  may  be  added  in  regard  to  the 
low  values  of  carbon  dioxide  found  in  the  tests.  The  writer 
makes  no  assumption  that  the  building  is  air  tight.  The  tests 
were  made  under  actual  conditions  as  they  exist  at  the  school. 
The  windows  are  of  such  construction  that  less  leakage  takes 
place  than  is  usual  in  most  school  buildings,  and  careful  observa- 
tions of  the  building  showed  that  none  of  the  windows  were  open 
during  the  test  or  during  most  of  the  school  year. 

But  of  course  leakage  took  place,  and  in  accounting  for  the  low 
values  of  carbon  dioxide  found,  the  following  points  must  also 
be  borne  in  mind  : 

Room  No.  15  (see  Table  I),  which  is  the  gymnasium,  was  oc- 
cupied only  late  in  the  afternoons,  and  whatever  leakage  that 
took  place  into  this  room  during  the  day  was  distributed  through 
all  the  other  rooms  of  the  building  by  means  of  the  recirculating 
system. 

The  same  is  true  of  the  Auditorium,  Room  No.  214.  The 
Auditorium  was  used  only  for  assembly  periods  two  or  three 
times  a week  and  then  only  for  an  hour  a day.  At  all  other 
times  the  leakage  into  this  large  room  was  distributed  through 
all  the  other  rooms.  And,  during  assembly  periods  all  the  class- 
rooms are  unoccupied  and  a large  part  of  the  leakage  into  them 
finds  its  way  into  the  Auditorium. 

The  same  action  takes  place  from  Rooms  No.  108  and  No.  209. 
These  rooms  are  small  auditoriums  which  are  only  used  for 
short  periods  once  or  twice  a week. 

There  was  an  average  attendance  of  about  250  students  in  the 
building  throughout  the  school  year.  The  figures  in  Table  I are 
based  upon  the  student  capacity  of  the  rooms  and  not  upon  the 
actual  attendance. 

The  average  attendance  for  the  year  for  the  various  class  rooms 
is  given  below. 


* Added  on  the  recommendation  of  the  Publicatiton  Committee. 


Tests  on  the  Recirculation  of  Washed  Air 


43 


Room  Number 

Student  Capacity 
of  Room 

Average 

Attendance 

8 

20 

16 

10 

28 

16 

106 

26 

20 

107 

26 

11 

109 

26 

20 

115 

31 

26 

207 

31 

22 

208 

26 

17 

210 

26 

20 

211 

31 

23 

218 

20 

17 

308 

41 

20 

309 

25 

16 

311 

15 

14 

312 

14 

14 

314 

29 

16 

Average  26 

Average  18 

